After putting the truck back together had issues with bubbles constantly flowing in the reservoir, I knew I had an issue with a head. So I had the heads redone and put everything back together for the 2nd time with better results. Everything seems to be fine with the temp and running. But after a second trial run after about 5 minutes of driving the check engine light came on. Went home and checked the codes. 543 and 172. Any ideas? I know what the code descriptions are, but anyone have an idea where to start?